[FEATURE] Quote-reply to a specific earlier message (claude.ai/code and mobile app)

### Preflight Checklist
- [x] I have searched existing requests and this feature hasn't been requested yet
- [x] This is a single feature request (not multiple features)

### Problem Statement
In long sessions (hundreds of turns), especially when continuing from the phone or browser through Remote Control, there is no way to point at the specific earlier message I am responding to. The model still has the whole context, but I have no affordance to say "this one". Today I either copy-paste a fragment into the prompt, which is slow and error-prone on mobile, or I describe the message in words ("the table", "the long message from earlier"), which is ambiguous when the conversation has many similar parts.

### Proposed Solution
A WhatsApp-style quote-reply on message bubbles in claude.ai/code and in the iOS/Android app:
- swipe / long-press / hover action "Reply" on any bubble (user or assistant);
- optionally, select a text range inside a message and "Reply to selection";
- the quoted excerpt is shown above the composer and sent along with the new prompt as a structured reference (message id + excerpt) so the model knows exactly what is being answered, and it is rendered as a quote block in the transcript.
A lighter equivalent in the terminal TUI could be a `/reply` picker over recent messages.

### Alternative Solutions
- Copy-paste the fragment manually (current workaround; clumsy on a phone).
- Describe the message in words and rely on the model to guess.
- Chat apps (WhatsApp, Telegram, Slack threads) solve this with quote-reply; the same affordance would fit here.

### Priority
Medium - Would be very helpful

### Feature Category
Other (claude.ai/code web client and mobile app; TUI equivalent optional)

### Use Case Example
1. A long analytical session on the desktop app, several long assistant answers with multiple paragraphs.
2. I continue from the phone through Remote Control.
3. I want to push back on one specific paragraph from an answer given ten turns ago.
4. With quote-reply I swipe on that paragraph, type two lines, send. Today I have to scroll, copy, paste, then type.

### Additional Context
Session was on Claude Code 2.1.241, desktop app (Code tab) plus Remote Control from the mobile app.

The request covers claude.ai/code, iOS and Android apps, Remote Control, and an optional terminal TUI; begin by mapping which client owns message bubbles, the composer, transcript rendering, and message transport. Confirm the product scope and structured-reference contract first; done means a selected earlier message can be quoted and identified in the new prompt across the agreed clients.

索引モデルが issue の本文から書いたものです。